libcxx/include/__compare/common_comparison_category.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___COMPARE_COMMON_COMPARISON_CATEGORY_H
  10 #define _LIBCPP___COMPARE_COMMON_COMPARISON_CATEGORY_H
  11
  12 #include <__compare/ordering.h>
  13 #include <__config>
  14 #include <__type_traits/is_same.h>
  15 #include <cstddef>
  16
  17 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  18 #  pragma GCC system_header
  19 #endif
  20
  21 _LIBCPP_BEGIN_NAMESPACE_STD
  22
  23 #if _LIBCPP_STD_VER >= 20
  24
  25 namespace __comp_detail {
  26
  27 enum _ClassifyCompCategory : unsigned {
  28   _None,
  29   _PartialOrd,
  30   _WeakOrd,
  31   _StrongOrd,
  32   _CCC_Size
  33 };
  34
  35 template <class _Tp>
  36 _LIBCPP_HIDE_FROM_ABI
  37 constexpr _ClassifyCompCategory __type_to_enum() noexcept {
  38   if (is_same_v<_Tp, partial_ordering>)
  39     return _PartialOrd;
  40   if (is_same_v<_Tp, weak_ordering>)
  41     return _WeakOrd;
  42   if (is_same_v<_Tp, strong_ordering>)
  43     return _StrongOrd;
  44   return _None;
  45 }
  46
  47 template <size_t _Size>
  48 _LIBCPP_HIDE_FROM_ABI
  49 constexpr _ClassifyCompCategory
  50 __compute_comp_type(const _ClassifyCompCategory (&__types)[_Size]) {
  51   int __seen[_CCC_Size] = {};
  52   for (auto __type : __types)
  53     ++__seen[__type];
  54   if (__seen[_None])
  55     return _None;
  56   if (__seen[_PartialOrd])
  57     return _PartialOrd;
  58   if (__seen[_WeakOrd])
  59     return _WeakOrd;
  60   return _StrongOrd;
  61 }
  62
  63 template <class ..._Ts, bool _False = false>
  64 _LIBCPP_HIDE_FROM_ABI
  65 constexpr auto __get_comp_type() {
  66   using _CCC = _ClassifyCompCategory;
  67   constexpr _CCC __type_kinds[] = {_StrongOrd, __type_to_enum<_Ts>()...};
  68   constexpr _CCC __cat = __comp_detail::__compute_comp_type(__type_kinds);
  69   if constexpr (__cat == _None)
  70     return void();
  71   else if constexpr (__cat == _PartialOrd)
  72     return partial_ordering::equivalent;
  73   else if constexpr (__cat == _WeakOrd)
  74     return weak_ordering::equivalent;
  75   else if constexpr (__cat == _StrongOrd)
  76     return strong_ordering::equivalent;
  77   else
  78     static_assert(_False, "unhandled case");
  79 }
  80 } // namespace __comp_detail
  81
  82 // [cmp.common], common comparison category type
  83 template<class... _Ts>
  84 struct _LIBCPP_TEMPLATE_VIS common_comparison_category {
  85   using type = decltype(__comp_detail::__get_comp_type<_Ts...>());
  86 };
  87
  88 template<class... _Ts>
  89 using common_comparison_category_t = typename common_comparison_category<_Ts...>::type;
  90
  91 #endif // _LIBCPP_STD_VER >= 20
  92
  93 _LIBCPP_END_NAMESPACE_STD
  94
  95 #endif // _LIBCPP___COMPARE_COMMON_COMPARISON_CATEGORY_H